1. Field of the Invention
The present invention relates to an extrusion type coating head that is used for applying, for example, magnetic coating onto a support.
2. Description of the Prior Art
Conventionally, when a magnetic recording medium is produced by applying a coating solution such as a magnetic paint on a non-magnetic support, for example, various coating methods have been adopted such as gravure, reverse, extrusion, and doctor blade coating methods.
Among them, the extrusion type coating method is in particular characteristic in that a very uniform thin film is obtained even if the film thickness in wet condition is 10 .mu.m or less, and suitable for a precise thin film coating. Thus, the extrusion type coating method has been noted for a very suitable coating method as a production process of a magnetic recording medium that requires a thin film coating for the purpose of high density recording. Therefore, extrusion type coating heads used in this coating method have been proposed heretofore.
In particular, in the Japanese Patent Laid-open Publication Nos. HEI 2-207865 and HEI 2-207866, and Japanese Patent Publication Nos. SHO 55-35990 and SHO 49-1459 proposed are coating methods and/or coating devices that prevent coating defects such as streak development and unevenness on coating surfaces.
In the Japanese Patent Laid-open Publication Nos. HEI 2-207865 and HEI 2-207866, proposed is a coating device in which a coating solution is delivered from a nozzle to apply the solution to the support to be coated; in such a device, the center line average roughness of the back edge surface is controlled, or the straightness of the waviness component of the front and/or back edge surface is controlled for preventing generation of streaky coating unevenness and other streaky coating defects.
While the coating thickness becomes uniform in the longitudinal direction in the coating of the base film by these devices, however, the coating thickness in the direction of width tends to be uneven; in addition, wrinkles and inclined elongation often develop in the tape itself when wound on a roll since the coating thickness varies. This not only reduces the productivity (yield) substantially but also deteriorates the product quality, particularly causing the fluctuation of output level and decrease of skew; thus, further improvement of the coating quality is desired.
Japanese Patent Publication No. SHO 55-35990 disclosed a cascade type coating device having a gap for supplying the coating solution, and Japanese Patent Publication No. SHO 55-35990 disclosed a tubular type coating device, in particular one having a slit opening of a special shape; both of these were proposed for the purpose of obtaining uniform coating thickness.
However, these devices do not give satisfatory coating quality such as uniform coating thickness, as are the cases mentioned above. Further improvement is required particularly for overcoming uneven coating and getting better uniformity in the film thickness of the width direction.
The present invention has been made under such situation and aims to improve coating surface quality, in particular to improve unevenness and unsteadiness in the film thickness of the width direction, thereby preventing development of wrinkles and inclined elongation in the tape itself when wound on a roll, improving the productivity, and reducing adverse effects (for example, fluctuation of output level and decrease of skew) to the product quality.